1. Field of the Invention
The present invention relates generally to a flow rate controller, and more particularly to a method of and an apparatus for controlling the flow rate of a fluid by compressing a resiliently deformable fluid path portion or releasing it from the compression.
2. Description of the Prior Art
As shown in FIGS. 24(a) and (b), a typical flow rate controller that is known to the relevant art, generally designated by 187, includes a fluid path 182 inside which a resiliently deformable sleeve 183, or simply a resilient sleeve, is mounted. In this construction, the resilient sleeve 183 has peripheral marginal edges 184 and 185 on the opposite sides thereof rigidly fixed to the inner wall of the fluid path 182, with a hollow space 186 formed between the inner wall of the fluid path 182 and the resilient sleeve 183. The flow rate of a fluid may be controlled by increasing or decreasing the pressure to be applied to the hollow space 186 to thereby vary the shape in cross section of the resilient sleeve 183.
According to the flow rate controller as described above, the fluid path 182 is completely closed by compressing the resilient sleeve 183 under pneumatic pressure applied thereto, as shown in FIGS. 24(c) and (d). This may disadvantageously cause fluid leaks or escapes through the compressed fluid path. Particularly when the fluid flows under high pressures, more leaks or escapes may occur. Furthermore, when the resilient sleeve 183 is placed in its intermediate (half open) state between the fully opened state, and fully closed state when the fluid flows under high pressures (FIGS. 24(a) and (b)), the resilient sleeve 183 may suffer small vibrations which cause the fluid to flow therethrough at varying rates.